The present invention relates to an apparatus and method for injecting tubing into a well utilizing a drive chain, and, more particularly, to such an apparatus and method for monitoring stretching of the chain. The phrase “chain stretch” or “stretch” is commonly used in the industry to indicate the net lengthening of the chain due to wear of the members (rollers, pins, etc.) comprising the chain. Stretching does not mean that the metal members of the chain have elongated due to elastic or plastic deformation.
Coiled tubing injectors are often used to inject coiled tubing into an oil or gas well to facilitate the servicing of the well. These injectors usually include a pair of chains that extend to either side of the coiled tubing, and gripper blocks mounted to the chains for engaging the coiled tubing and driving it into the well. Also, depth indicators are often used that engage the chain and provide an indication of the depth of the coiled tubing based on the movement of the chain.
However, the chains can stretch with use and age, leading to ultimate failure of the chain, and, in the meantime, causing erroneous readings from the depth indicators.
Therefore, what is needed is a system and method for monitoring chain stretch so that the above problems can be avoided.